"When you love racing this is very hard," said the 26-year-old Frenchman. "I accept my mistake."
Grosjean maintained he did not intend to squeeze Lewis Hamilton's McLaren towards the pitwall on the inside, prior to the contact that caused them both to collide with Fernando Alonso's Ferrari and both Saubers.
"We know that La Source is a very tough corner. It was a bit of a crazy start as well with [Pastor] Maldonado leaving [the grid early] and the Sauber [Kobayashi] smoking a lot," said Grosjean.
"I did a mistake and I misjudged the gap with Lewis. I was sure I was in front of him. So a small mistake made a big incident.
"I didn't change my line, I went from left to right. I was not really wanting to put anyone in the wall - I'm not here to stop the race in the first corner. I'm very, very sorry and I'm glad that nobody is hurt.
"But I have to say it is a very, very hard decision to hear."
Grosjean, who has been involved in five early-race incidents this year, said he was more angry with himself than with the penalty, but added that the accidents were not all caused by over-aggression.
"I did too many," he said. "If there is more than one then that is too many, I agree. But as I say it is not always the same. It's not over-aggressive by braking 200 metres too late, it's just most of the time misjudgement of the space I have in front or the space I have on the side.
"It's true that we don't see much in the mirrors and stuff like that and it goes very quick at the start.
"I was to be honest 100 per cent sure I was in front of Lewis but I was not so I need to rethink about my view of the car.
"I am the most angry at myself to have misjudged the gap with Lewis's car."
Grosjean said that his focus now was on analysing what led to the ban and to ensure that the rest of the season continues without error, adding that he hoped it would not affect his chances of keeping his drive with Lotus in 2012.
"It is too much. I know that. Some are not my fault, but yeah I will analyse that and I will try to not repeat it in the seven last races," he said.
"For sure I don't want to do any more [crashes] by the end of the season. So I will work, I will analyse as much as I can to try and avoid those. Some were misfortune, some were my mistake but now it is time to finish that."
Pastor Maldonado, meanwhile, will be demoted 10 places on the grid as a punishment for both jumping the start in Belgium and colliding with Timo Glock.
The Williams driver had already been given a three-place grid penalty at Spa for blocking Nico Hulkenberg in qualifying.
He then made a premature getaway in the race, before being tagged into a spin as the crash involving Grosjean, Hamilton, Alonso and the Saubers unfolded.
Maldonado rejoined, only to collide with Timo Glock's Marussia at the restart, ending his race.
Although Glock was able to continue, the stewards ruled that Maldonado's actions in the clash deserved a five-place penalty.
They also bestowed an additional five-place drop as he had been unable to take the usual drivethrough penalty for a jump-start in the race due to his early retirement.
"The driver failed to finish the race so the usual penalty for a false start could not be imposed," said an official statement.
Maldonado accepted the blame for the start error.
"I made a slight mistake at the start because the clutch slipped out of my hands before the red light switched off," he said.
- Lewis Hamilton