That's right, and the only purpose I always think of is to have a safe flight.
That's good if you're not actually going anywhere, otherwise the purpose is to get where you're going safely.
I have, over the years, developed a 3-count rule.
Any mistake I make, or any difficulties I find, or any discrepancies, no matter how small, counts in the 3-count rule, and if I get to 3 before takeoff, then I terminate the flight - my mind isn't fully focused obviously - go have a cup of coffee and evaluate my mental condition.
For example, the last flight I took I left the keys in my pocket before I got into the plane (hard to get them out when sitting) - that counts.
Ever left the chocks or tie-downs? that's another one.
Forgot the frequency of the tower? yet another.
After takeoff, I reset the counter to zero. If it gets to 3 in flight, then I make sure I'm in a safe location and straight and level, and then have a good chat with myself to make sure I'm paying attention.
These are NOT major mess-ups. If I make a major mess-up, then I immediately check myself, either don't take off, or make sure I can work on my mental state.
By counting them, I've found that I've taught my mind to look for them, and to flag them up whenever something happens, and that has made me more alert to issues.