When problem A reduces to problem B, which problem is more complex?
When we reduce $A$ to&nbsp;$B$, we are saying "If I could solve&nbsp;$B$ in some model of computation, then I could solve&nbsp;$A$ in that model, too" (as long as the reduction is sufficiently simple that it can be performed within the relevant model of computation).

This means that $B$&nbsp;is at least as hard as&nbsp;$A$. But $A$&nbsp;could be easier &ndash; much easier. For example, let $A\in$&nbsp;P and let  $B$&nbsp;be any EXP-complete problem. Because $B$&nbsp;is EXP-complete, every problem in EXP reduces to&nbsp;$B$ so, in particular, $A$&nbsp;reduces to&nbsp;$B$. But we know that $A$&nbsp;is strictly easier than&nbsp;$B$ by the time hierarchy theorem.