The Oranje boss has criticised his team's individual errors, but hopes they can learn from their mistakes, while Wesley Sneijder and Arjen Robben also commented on the loss
Goals from Christian Benteke, Dries Mertens, Romelu Lukaku and Jan Vertonghen forced the newly-appointed coach to start his second spell in charge of the Oranje on the back foot, and he lamented his players' lack of organisation.
"We lost because of personal mistakes," the Dutch trainer told SBS 6. "The first half wasn't good because we played sloppy when we had the ball."
He also singled out Manchester City midfielder Nigel De Jong for criticism: "At half time, I said to my players that Nigel de Jong should stay away when we had the ball.
"We started the second half very well, but due to personal mistakes we threw away the match. Especially the second goal, that was a big mistake by De Jong."
Van Gaal hoped Netherlands could take positives from the result, however, saying: "We can learn from this match. We had a very young squad and Belgium is a good team. They are more experienced then us."
Meanwhile, Inter midfielder Wesley Sneijder was also critical of his team's individual errors: "We didnt play well in the first half.
"The second was a lot better, but we gave it away with two personal mistakes by Nigel de Jong and Maarten Stekelenburg."
He added that he hoped a change in tactics could improve the national team's results: "I think that with a new team and a different system [4-3-3 instead of 4-2-3-1] we can be partly satisfied.
"We had to score more goals, but at some points in the game we really played very well."
Bayern Munich winger Arjen Robben echoed his colleagues sentiments, claiming: "We can learn from this match and we have a lot of work to do."