A good robot vacuum will keep your floors in a near-constant state of tidiness: No stray dust bunnies begging to be cleaned up, no crumbs stuck to the bottom of your feet. Most people who own a bot will say that it makes their life a little better.

But those same people will also tell you that their bots aren’t perfect—and some people can just never get comfortable with their flaws. We cover all of the details in our comprehensive guide to robot vacuums, but here’s the short version of all the ways that a robot vacuum might let you down:

1. They don’t really clean carpets, at least not like a proper vacuum can.

Bots are great for bare floors and can keep carpets feeling clean because they pick up obvious junk like crumbs, road grit, cat litter, and some pet hair (as long as it hasn’t been walked all over and ground into long carpet fibers).

But over time, your rugs will end up collecting plenty of hair and dust that a robot just can’t suck up. You may not see it, or feel it stuck to your feet, but the carpets will start to look dull over time, and your indoor air quality may suffer.

Even the strongest robot vacuums have a fraction of the raw cleaning power of an $80 upright vacuum, so you’ll have to bust out something stronger than your bot from time to time if you want truly clean rugs.

2. They can get stuck on the most mundane, unavoidable household clutter.

Modern homes are filled with obstacles that can snarl or tangle or otherwise trap your robot in the middle of a cleaning session. Charging cables are a guaranteed stopper, no matter how nimble your robot is. Stray socks (and other types of laundry) are almost as bad. Many bots struggle on tall or wide thresholds, and some can’t even climb from a bare floor onto a rug.

If you keep your floors clutter-free, your bot will run smoothly, for the most part. The most important step is to get in the habit of picking up your laundry and cords.

But in some homes, no matter how diligent you are about eliminating traps and obstacles, some bots will find a way to get stuck from time to time, and you’ll have to get used to rescuing them.

3. They don’t always look like they know what they’re doing.

If you sit and watch your robot while it works, you’ll see it do some stuff that looks really dumb: making weird turns, driving past an obvious mess, or stubbornly bumping into the same obstacles over and over again. It might spend 20 minutes cleaning the same small section of your house and then miss an entire room. Sometimes, it won’t even make it back to its dock to recharge at the end of a session.

Cheaper robots look clueless and get lost more often, but even the high-end models find plenty of ways to act foolish, too. We’ve found that bots with interactive maps (to help you set invisible boundaries) can really drive people nuts when they don’t work right.

We’ve found that the best way to relieve your frustration with a robot is to stop watching it work. Trust it to do its job, forgive it if misses a tuft of cat hair or quits before it gets back to its dock, and find something else to do with your time. That’s the point of buying a robot vacuum anyway, right?

4. They can smear poop everywhere.

If your dog can’t hold it, and your bot runs across the mess, you could have a turdpocalypse on your hands.

For a whole lot more on what bots can and can’t do—and our favorite models—check out our guide to the best robot vacuums. We really do think they’re useful, life-improving gadgets for most people in most homes!