The Blues paid £62M to sign him from Brighton, but he struggled to replicate his Seagulls form in his first two seasons.
Despite managerial changes, his performances dipped, but winning Euro 2024 with Spain helped revive his confidence.
Cucurella told La Media Inglesa: “When things started to get a bit complicated, it’s difficult because you start to notice that everything that happens is your fault.
“I remember a game, I think we lost, at Fulham. 2-1, I think, or 2-0. I played for five minutes or 10 minutes and (it was) my fault, you know. I say yes, I know, but I haven’t played. And then people boo me, this is also difficult.
“And I don’t know, you lose a bit of, above all, your confidence in yourself. I think this is the most important thing.
“It’s difficult, but ultimately I am working to reach a point where (I feel that) on the day you play well you’re not the greatest and on the day you play badly you’re not the worst.”