Should parents practice what they preach? how can a parent preach to the son about what he should have done with his life when the parent didn't do it

Rethink Preach: Aside from setting important boundaries, here are some thoughts.If we tell people what to do or what not to do, they often get resistant and push away. Rethink the preaching. Speak honestly about your fears for your son. Also work on making the personal changes you want to see in your family. You're the role model. Parenting is a tough job. Consider working with psychologist for help, support, etc.

From your question: It's not clear to me whether u are the parent or the son? Sometimes parents realize they have made mistakes in life and try to help their children avoid mistakes they have made. If they "preach" about it, it often makes their message sound phony. They may be trying to help and not know how. It's always better to practice what you preach, but recognizing mistakes and learning from them is 2nd best.

I agree, some : parents don't want their children to "rewrite their scripts", especially if they had behaviors that caused them harmful dysfunction in relationships, careers or financial security. Parents usually act out of love, even though they may not be able to express that very well & may give their children unsolicited advice or state their concerns in a way that the adult child feels is demeaning.