What does it mean when someone says "don't take life too seriously" ? What does it suggest ?

Hi, Alice123!

It can depend on the circumstance.

In general, from my point of view, it would mean that life isn't perfect and that the way that we might expect things to turn out are not necessarily the way that they will turn out, so it's best to not take life too seriously because not everything that happens in our lives is totally under our control, but might involve a number of factors.

So, if you can't control it, then why be worried or concerned about it? Some examples might be found via clicking on the following link. Que Sera Sera - Google Search

Whatever will be, will be, is just one example, though...

Is there a particular reason that you are asking the question, please?

Thanks!