They all kinda have to prove themselves outside probably Amir Johnson.
ET and Sully are playing for contracts, but they already earned a lot of $$ this season. The playoffs will influence that number, but I dont see it as crucial for them.
Youd love to see Smart have a coming out party, but no one is giving up on the guy (at least in the Celtics FO) based on a tough playoff series
AB has struggled in the playoffs in years past. Hes either been hurt(2012 I believe) or largely ineffective (2015 and 2013). This year hes shown tremendous improvement in terms of returning to that stud on ball defender from his early years, while also extending his range to 3pt territory and improving his handle and finishing abilities to the point where he is a subpar shot creator as opposed to a nonexistent one. exorcising those playoff demons would go a long way for his rep and place as a leader and long term fixture within the Cs but ultimately he is so well thought of in the Cs organization a tough playoff stretch isnt a big deal I dont think.
Like any breakout player Crowder will look to add legitimacy to his season, but with the ankle and his performance last year in the playoffs I think he has the least to prove.
Isaiah THomas has the most. He has been doubted at every stage, and at every stage he has proved his doubters wrong except for the playoffs. ISaiah has been there once, and when he got there he was terrible. This is likely because he was the only quasi competent scorer on the team and the Cavs just completely focused on him, but it doesnt matter. When you are 5'9" you dont get the benefit of the doubt. If he wants to be a star in this league, he has to prove it in the playoffs. This is his shot. He has a lot to prove.