"It's live every week and if I made a mistake [the press would say]: 'Oh he's 86 years old and past it'," Sir Bruce said.
Two weeks ago Sir Bruce confirmed he would be stepping down from hosting Strictly Come Dancing with Tess Daly.
Bruce Forsyth at 2013 Strictly Come Dancing red carpet launch
The BBC Strictly Come Dancing twitter feed confirmed his departure, tweeting: "After 10 wonderful years & 11 series, Sir Bruce Forsyth has decided to step down from the rigours of presenting our live shows", before adding: "Sir Bruce is one of the great showbiz legends of our time and our succesd is due in vast amounts to him. This is not farewell!"
The presenter and entertainer, whose career has spanned 74 years, will continue to present the special episodes of the show, including the Christmas and Children In Need specials.
Speaking to Michael McIntyre on his chat show, Sir Bruce said he had to "think very seriously" about leaving the show but admitted that he knew "it's better for me".
After 10 wonderful years & 11 series, Sir Bruce Forsyth has decided to step down from the rigours of presenting our live shows.— BBC Strictly (@bbcstrictly) April 4, 2014
Here's a little Brucie bonus for you. It's a promise Sir! pic.twitter.com/HNhP24Fh8d— BBC Strictly (@bbcstrictly) April 4, 2014
The 86-year-old added: "It comes to a time when you do get to a stage and say 'this is enough'. And I do get tired doing live telly. Live telly is very, very strenuous, especially when some of the shows are an hour and 40 minutes long."
"It was a big decision... It's better for me physically, I'll be able to spend more time with my wife and my family."
Following the news, Tess led some of the entertainment world’s best stars plus numerous ex-Strictly judges and contestants in praising Sir Bruce.
"He's a TV legend, a total gentleman and someone my family and I are honoured to call a true friend", Bruce’s co-host said.
Bruce Forsyth and Tess Daly at 2013 Strictly Come Dancing red carpet launch
Speaking of the reaction, Sir Bruce said: "I didn't expect it to make all the fuss it did. I'm very flattered by all that and it's been marvellous."
Odds are already on for who should replace Sir Bruce, with Claudia Winkleman reportedly being "first choice" for producers.
But Sir Bruce admitted he has no idea who the BBC will pick.