At its core, soccer is about figuring out ways to put the ball into your opponent's net more often than they put it in yours. There are all kinds of stylistic and strategic ways of going about that, but over the long grind of a 38-game season, the teams that score more than their opponents are almost always the teams that create more and better opportunities than they allow.
With a game to go in the Premier League 2022-23 season, Southampton are the only side to have been officially relegated. They have the fewest points (24) and the worst goal differential (-37). That'll do it, every time. And although they're still technically alive, Leeds United and Leicester City are both heavily favored to join the Saints in the Championship next season. Leicester have the 14th-best goal differential (-18), and they're two points behind 17th-place Everton (33); Leeds, and their 17th-best goal differential (-27), are also two back on 31 points.
However, none of the three have been that bad at controlling the balance of chances. Southampton generated 45% of the shots in their games; Leeds are up at 46% -- 14th and 13th respectively. And it's not like they're all giving up breakaways and shooting from midfield, either. By Expected Goal (xG) differential, which combines the quantity of shots with the quality of shots, Southampton rank 17th, and Leeds rank 15th. Although Leicester have the third-worst shot ratio (42.1%), they have the 14th-best xG differential.
There are many reasons why these three teams are likely to be relegated, some inside their control and plenty of others outside it. But in terms of tangible things we can point to, perhaps the unifying factor behind their poor seasons is that they couldn't save any shots.