Forget all the hearts you're seeing around Valentine's Day: your heart shouldn't guide your financial planning.

Emotion and money seldom make great bedfellows. According to the folks at finance site NerdWallet, 49% of Americans say emotions have caused them to spend more than they can afford. That wears off a bit with age -- 67% of Millennials (18-34) say so vs. 29% of Baby Boomers over 65 -- but everybody makes terrible emotional decisions with money.

Of those who let emotions dictate their overspending, 29% say they overspend due to stress, 22% say it's because of excitement and 13% say it's retail therapy to cope with sadness. Though 86% think there are acceptable reasons to go into credit card debt, roughly that many (87%) would be embarrassed to do so. In fact, most Americans will feel terrible if they go into debt for any reason beyond covering emergency purchases (63%), medical expenses (61%) and covering necessary expenses during periods of unemployment (45%).

However, even a quick rush of endorphins from an uplifting event can inspire some rash financial decisions. Financial firm UBS Wealth Management Americas found that investors' outlook on the economy, their top concern during the 2016 Presidential election, has improved by 50% since Trump was elected. Additionally, 68% of investors said they expect Trump's policies to lead to strong stock market returns over the next six months. As a result, the majority of investors (55%) are actively looking for investment opportunities, up from 34% immediately following the election, with 42% likely to increase their investments in the stock market and nearly one-third of wealthy investors (30%) ready to deploy cash.

While those folks are anticipating pro-business policies (71%), lower taxes, decreased regulation and increased infrastructure spending (69%), it should be noted that none of the above have come to fruition just yet. In fact, fiscal policy hasn't even made it to the front of the line during the new president's earliest days in office.

"After years of caution following the financial crisis, we are finally seeing the tide turn. Investors are more willing to move cash off the sidelines and increase investments, while business owners are set to increase capital spending and hiring," says Paula Polito, UBS client strategy officer of WMA. "If the recent optimism continues, it will bode well for the markets and the economy."

Conversely, emotion-based pessimism can prove detrimental to finacial planning. Trump supporters are more likely than Clinton supporters to be optimistic about S&P 500 returns in the next six months (90% vs. 44%), though stock market optimism across party lines has increased from 25% before the election to 68% in January. Trump supporters' optimism improved from 25% prior to the election to 79% post-election, Democratic candidate Hillary Clinton's supporters, meanwhile continue to be wary of Trump's unpredictability (87%) and his potential business conflicts (80%), and the impact they can have on social issues and America's standing in the global competitive environment. As a result, only 41% tend to be optimistic about their investment options.

That trepidation isn't unjustified, at least in the short term. Tom Elliott, international investment strategist at U.K.-based deVere Group, notes that market volatility is perfectly normal within the first 100 days of a new presidential administration. Considering the outgoing administration left the economy growing at an annual rate around 3.5% a year -- faster than any developed country other than Canada -- and put unemployment at 4.7%, it may be tough to improve upon that growth through new policy.

"It is Trump's fiscal policies that most analysts worry about, should Congress pass them, he says. "The type of fiscal stimulus policies that Trump has promised, such as lower taxes and infrastructure spending, can make up for shortfalls in public spending and so stimulate a depressed economy. Yet the U.S. is not suffering from a depressed economy, and inflation may be the result."

Yet even seemingly cerebral decisions related to market performance, federal policy and economic growth can be tainted by emotional impulse if investors don't take a breath. Investor psychology has a few key emotional triggers and has maintained them throughout history.

"It hasn't changed since the tulip mania in the 1600s, or even since money was invented," says Benjamin Sullivan, certified financial planner and portfolio manager with Palisades Hudson Financial Group in Austin, Texas. "The roller coaster of the stock market makes for a lot of adrenaline, euphoria and fear—a recipe for bad decisions."

Hot funds or stocks don't typically keep climbing. Securities that have plummeted don't always go lower. Yet when there's a financial crisis like the one in 2008 and 2009, investors go bailing out of stocks immediately. It's called recency bias, and it leads to hasty, emotional choices based on irrelevant data.

"We're all prone to pay undue attention to recent news, either good or bad, and underemphasize long-term trends," Sullivan says. "Performance in the recent past is arguably the least useful information about an investment. But recent performance data is easy to understand and dramatic."

Hot funds or stocks aren't guaranteed to keep going up. The opposite is often the case. Securities that have plummeted aren't a sure thing to go lower. However, these aren't the only lessons that both your heart and your head need to learn, if previous behavior is any indication.

You get overconfident in your investment abilities and throw too much of your portfolio into one stock. You invest heavily in an area you're familiar with instead of diversifying your portfolio. You either change your portfolio when markets are falling and everyone's making moves or hang on to your losing stock too long. Even worse, you try to time the market, jump on the next hot trend and avoid the next meltdown based of various predictions.

"If some guru really had magical powers to predict the market, would he or she tell the world?" Sullivan asks. "Or would that person keep it a secret and make an enormous fortune?"

For your purposes, you need data and a plan. Sullivan suggests creating a written investment plan and to sticking to it. Focusing on long-term results and including a market downturn or a major investment's failure can help you avoid spur-of-the moment emotional reactions.

"We all make mistakes, but a plan that accounts for foreseeable problems can help protect you from avoidable missteps," Sullivan says. "If you know you can't stay disciplined, hire someone else to manage your money."