Pilots are supposed to do fuel calculations for every trip along with weight and balance.
A lot of pilots get lazy and don’t do it. Or they could make a simple math mistake.
At the airport my son and I fly out of, I69, a guy rented a Cessna 172 from Sporty’s Pilot Shop the other day. Loaded it with fuel and three buddies.
Never made it off the runway. Ran it off into a ditch at the end. He was 500 lbs overweight from the 980 max load. Just stupid. At least no one died in that one.
Don’t fill the tanks if you fill the seats.