PSG were stunningly eliminated from the Champions League on Wednesday, suffering a 3-1 loss at home to Manchester United to bow out on away goals after a 3-3 aggregate draw.
But it took a contentious 94th-minute penalty to send United through, Marcus Rashford converting after a VAR review led to Presnel Kimpembe being penalised for a handball.
A measured Tuchel rued the decision as PSG were eliminated in the last 16 of the competition for a third straight season.
"It was a big decision, a cruel decision... but it's difficult. There are reasons he can give the decision. It's always soft facts with hands," he told a news conference.
"The shot is not a big, big chance. It's wide, then suddenly it's a penalty."
Romelu Lukaku's brace in the first half gave United hope, but Juan Bernat's 12th-minute goal had PSG on track before the late drama.
Despite the VAR intervening, Tuchel said he still supported the use of the technology, acknowledging the handball rule was a difficult one.
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"I'm a big supporter of VAR, and I am still a big supporter of VAR," he said.
"With hand, it's a super-difficult thing, because there are too many points in do we punish it or not punish it, distance, natural position... so many things to discuss.
"I think [it's] a 50-50 decision."
Tuchel added: "This is the problem with hand. The points people use to support the decision say it isn't.
"For a shot that was going 50 metres over the bar to get a penalty from 11 metres, there is no logic in that."