Two dumb things i have done was replacing the rear wheel on my old HQ statesman many years ago. carefully tapped the bearing on then carefully tapped the bearing retainer on , then carefully looked at the bearing seal on the ground that i forgot to put on before the bearing and retainer . The other one was replacing the transmission lines on the same car using a ring spanner ,not realising that when both ends are connected there is no was to get the ring spanner off . It's amazing the uses you can find for cable ties.
there are three types of people in the world , those who can count and those who can't