This is typically something we say to someone who does something hard successfully with minimal effort. It seems like a paradox. We expect hard things to require significant effort.
Therefore, success is dependent on matching my effort level with the difficulty of the task at hand. This does not consider the value of effort over time. Effort over time has the potential to compound. We call this skill.
Skill is the inherent ability without the use of additional effort. It is preferable to trade-off effort (high input/low output) for an increase in skill (low input/high output).
Unfortunately, skill takes time to develop. We do not see the yields as quickly as we do for increased effort. And so, we focus our effort on producing outcomes instead of increasing our skills. Certainly, skills we increase as a secondary benefit but it will do so much more slowly and will tabletop far below your potential.
The person who makes it look easy is the person who lagged behind the curve for a while, building something that will continue to deliver consistently for a long time, with ease.
It was not easy.