The teams don't suddenly become better, they just fight harder, and its happened time and again with many great escapes on the final day. It's a fairly universal truth in sport that when the chips are down, teams can pull out exceptional performances - even if they've been terrible all season.
For them as well as us, its about belief and not giving up until the end.
Its also partly because many teams who are rubbish over the course of the season still feel that can be giant killers on any given day in a one-off performance. Football has had many many upsets over the years, and many much less fancied teams have beaten heavily favoured teams in cup competitions, or the final day of the season etc.
Yes it is an uphill battle for a relegation threatened team to upset Man City but one thing we can be sure of is that we won't see this passive crap from Brighton on the final day, if they are still in the mix for staying up. So far, we've seen a number of games against City of late where their opposition just sit back and barely contest the game. City have had no resistance and even then they've hardly cruised to victory.
Of their remaining games, Man Utd will fight desperately for a Champions League spot, and a bit of pride after being thumped by Everton. Brighton need every point if they want to stay up, and will fight tooth and nail at home on the last day. Leicester and Burnley have less to play for but I'd say both are absolute banana skins. One is against a Rodgers team, who will want to prove they can cut it with the best. Burnley at Turf Moor can be a frustrating, turgid affair and they are unbeaten in 4 games and a tricky team to get past with their physicality and application.
They are 4 really tough games in my opinion and to be honest, if City get 12 points from 4 games then they fully deserve to win the title. They have had remarkable form since January and won every league game. It's never over until the final whistle, and I still expect some drama to unfold yet. IMHO, I think Man Utd will get a point at Old Trafford, and I think Burnley will upset them at Turf Moor and get a point.