That's why you have to check as much as possible before starting it the first time... Then double and triple check before you start it so you don't have to shut it down...
I helped a friend start a fresh rebuild and we found out one of the trans lines were leaking like a sieve and had to shut it down and fix the line... Then topped off the coolant and trans fluid and restarted it... Then the carb bowl was flooding over on a 'fresh rebuild carb'... There's always something to go wrong that you have to react to during first start and break in.... Very rarely do things go smoothly on the first try....