Thousands of couples will celebrate a day of romance this week, while many single people will hope for their own one. But what makes a relationship last? And what makes one couple crumble while another becomes stronger?

There are some psychological theories that can explain romance and relationships. Theories of love and romance are often misinterpreted as cold or callous. But knowing the physics behind rollercoasters does not reduce their thrill and excitement. In the same way, the thrills, spills and romance of relationships exist far beyond the theories.

The formation of a relationship is arguably the one of the most special moments. Life seems a little brighter, a little happier, and a lot more beautiful.

Sadly, for most, this only usually lasts for a matter of rose-tinted weeks, until the honeymoon period wears off and reality seeps back in. The halo is removed, and the effect is diminished. It is at this stage that arguments usually begin, which, while not inherently unhealthy, can become so if they go unresolved.

Some do find the resolution; others find their constitution – to continue. For those that do continue, the question psychologists often face is: why maintain an unhealthy relationship? It is to this question that psychological theories can shed some light.

The gambler’s fallacy

A man sits at a casino table, having lost a small fortune over a large amount of time. He mutters to himself: “my luck will change soon”. A woman sets out to go to work and sees it’s raining. Her car won’t start, and her umbrella is broken. Forlornly, she whispers: “surely, no more bad luck can happen”.

In both cases, this is the gambler’s fallacy at work – the belief that runs of bad luck cannot last. This same effect can be used to explain why someone in a relationship continues to hope the relationship improves despite long periods of dysfunctional interaction.

In nature, previous events seldom predict the future. In human nature, our past strongly predicts our future.

Confirmation bias

Even when confronted with overwhelming evidence to the contrary, you still believe what you want, and this belief is an impenetrable fortress. An overarching explanation for why people will not quit at relationships is our own ego. Implicitly, when we make most choices, we believe we are correct.

To justify our choice, we then seek information to support it – sometimes dismissing or denying evidence to the contrary. Religion’s representation of miracles is an example of this.

Irrespective of the myriad examples that falsify a claim, the one example that supports it is heralded and exaggerated. The scales should be weighed and judged equally.

Loss aversion

After some time, the relationship may have effectively broken down. Friends, family and the voice in your head are calling for a break-up. But some people still will not end their relationship.

Why? Notable, Noble-prize winning economists developed the theory of “loss aversion” to explain people’s behaviour in winning and losing situations. On the one hand, having a dysfunctional relationship is a harmful, hurtful experience. However, usually by this stage, a person’s self-concept is so merged with their partner that being single seems worse still.

Studies have shown that our self-esteem can become dependent on a partner, and so losing a loved one really is like losing a part of you.

But tearing a band-aid off quickly hurts less in the long-run.

The psychology of romance can go a long way to explaining why some people maintain commitment to a relationship that seems to have broken down. Ultimately, few relationships are all smooth sailing, and no success achieved ever came easily. The journey is long, and at times a struggle.

However, always be willing to openly ask yourself: what would I advise a friend in my position to do? Some psychological theories can help us understand why some people stick with rough relationships and try to ride out the storm. Even the best explanations and theories, however, cannot explain what it is to see colours or enjoy rollercoasters.

Given the unpredictable, irrational nature of humans, maybe all you need is love.