Why are the celtics doubted... when they first came together i admit i had some doubts despite being a cs....?

fan (not very fun back then, stadium was empty both games i went to that season)didnt think they had depth, thats what everyone else said too, but they proved they have sufficient, if not very good depth with their contributions from guys like house and posey. people then said they wouldnt be able to handle the west, and that theyd fall apart with an injury, but they beat the spurs 2 times without garnett and the second time allen (after a 22 point deficit), blew out the best team in the west coming off one of the best streaks ever.and the final criticism, they wont be the same in the playoffs, but this i admit is a reasonable doubt, cause the playoffs are different(though many of the veterans have playoffs experience,-yet im not saying that they will be unstoppable in the playofs or win the finals for sure,(im scared of the lakers to be honest) but what have they done to suggest they wont be good in the playoffs? all im saying is they havent done anything to merit doubt.