If you want to grow a tree that produces delicious apples, you cannot just fix the tree and have a result.
Instead, you fix everything around it produce the crop. You plant it in sunny place, give it water and nutrients and prune the tree where necessary. You guard the tree from bunnies and parasites and prevent weeds from taking over the roots.
Very much the same way a tester does not fix the product.
Instead, the tester produces information and serves it in an actionable way so that the team may produce a bountiful harvest.
Testing is improving things through others!