Alex Ferguson won 38 trophies in 26 success-laden seasons at Manchester United and the task of following in his footsteps proved too much for his immediate successor David Moyes.
Moyes was sacked in less than a season after breaking a host of unwanted records as United finished seventh in the Premier League campaign that ended in May.
"I had to follow Bobby Robson at Barcelona and that year he won three titles," Van Gaal told reporters on Monday during the club's pre-season tour of the United States.
"I have been at Ajax - the biggest club in the Netherlands - I went to Barcelona - the biggest club in Spain - and then I went to Bayern Munich, also the number one in Germany.
"So when Manchester United came I thought I had to say 'yes'."
Van Gaal's winning mentality and intimidating style has brought comparisons with Ferguson.
"I highly respect Alex because there is not another trainer or manager who has won so many titles," said the 62-year-old Dutchman who led his country to the semi-finals of the World Cup in Brazil earlier this month.
"I have won a lot of titles but he has won so many with one club and that is fantastic. When you compare Alex with me I am very proud."
Van Gaal said he would take his time before making up his mind on possible signings.
"I don't buy players for the sake of it," he explained. "I buy players to improve my selection.
"First I must see what I need in all the positions from the system we shall play and, at this moment, I don't know for sure."