Top teams stay at the top because they strike while the iron is hot. Feeling "comfortable" isn't an option; they are always looking to add quality to their squads where possible—even if it upsets the already successful status quo a little in the process.
Evidence of this philosophy can often be found in Catalonia, Spain, and 2018 has been no different so far. Despite opening up a 16-point lead over Real Madrid in La Liga and effectively sewing up a 25th title, Barcelona have forked out £142 million for Philippe Coutinho—a player who can’t even play for them in the UEFA Champions League latter stages.