What's the most common mistake young fools make?

Putting pineapple on pizza

That they are entitled to one fucking thing without effort.

Go get financed for a $30k car on minimum wage?

Not waiting for the right time

following their dreams... no seriously approachign a job that doesnt have a solid future.

its better to get a job you can tolerate and make a good living and live your dreams in your spare time instead of trying to make a living from your dreams butinstead earn money while making burgers.

by saying young fools that does not infer all young people are fools
so looking at the subset cohort

i would say perhaps:

arrogance leading to rapid reaction vs reasoning and understanding nuances

though this is an issue with adults of all age

Fools rush in where others will not.

Risk taking

Thinking they know it's love