The veteran striker has a deal to 2026 and is already in his fifth year on the south coast.
"I wouldn’t say surprised but no I probably didn’t expect to be here five years on," he told the Daily Mail. "Mental strength is… well I have read a few books that helped, but you also need to have that inner strength to be as good as you can.
"After an injury to my left knee I remember sitting there thinking: 'What can I do to really push on?'
"I worked out I could be watching analysing games. Like really look and see what I can do in different situations.
"Maybe some comes from my parents and I have two older brothers. As a kid I was fighting from a young age – not literally fighting – but fighting for approval and to make sure I was heard.
"And you do that until the road stops don’t you? And it’s important to enjoy it. A smile is never promised."
On being a senior leader inside the Brighton dressing room, Welbeck also said: "It’s very difficult for players not to get carried away.
"You have to differentiate between social media and real life and the reality of what happens here at the training ground.
"Football is a hard graft and yeah the lads talk in the dressing room. I try and tell them that there may be players in that room who don’t get as much social media attention or praise but what they have actually done to help us win a game is huge."