Do you feel all the lessons which life taught to you are actually helpful?

Rarely.
Life breaks down basically into two parts.
1. Things you are aware of.
What your responsibilities are
What you need to do
When you need to do it
How to go about it. Etc.

And

2. Things you are not aware of.
How you cope with certain situations once they make themselves known.
Who you need to consult about it.
How best to go about what you need to do.
What to do if, following that advice fails. Etc.

Sadly much of life is trial and error.
And it's easy to make the same mistakes.
And there are plenty of both

Bit of both, some times i have to repeat the lessons! Lol

I think lessons are this myth so we tolerate having a crappy time - "it's ok because I learnt something from it"

Most of them