The 48-year-old felt his side let itself down with its second half display after missing out on the chance to clinch the Ligue 1 title.
Victory would've seen the Ligue 1 leaders retain their title, but though Edinson Cavani got them off to the perfect start with the opener in the first half, the home side grew into the game in the second period.
It was rewarded for its efforts when Thiago Silva put the ball into his own net just shy of the hour mark, with PSG unable to find the goal that would've clinched the title.
"We didn't get the three points so there has to be disappointment. We missed a lot of chances and Sochaux produced a very good performance," Blanc said. "We scored a nice goal, but it wasn't enough. They came back into the game in the second half and equalized, but we didn't do enough, so a drawn isn't illogical."
PSG midfielder Yohan Cabaye added his disappointment at failing to clinch the league crown and pointed to a lack of cutting edge in the final third.
"We lacked success in and around the penalty area," he said. "There was more determination in the team that wanted to stay in the division than the one that wanted to lift the title.
"Unfortunately we are not champions tonight but we will stay focused and try and win against Rennes."