There is a general pattern in professional people.  We start out idealistic and adventurous, and as disasters inevitably accumulate we become more circumspect and pessimistic.

(Pre-emptive snarky response: "you say that like it's a bad thing.")

While pessimism is invaluable to a tester, it should be tempered with a just sense of hubris.  Larry Wall's saw about the three virtues of any great programmer has a historical antecedent from one of the canonical American authors:

We should be careful to get out of an experience only the wisdom that is in it -- and stop there; lest we be like the cat that sits down on a hot stove-lid. She will never sit down on a hot stove-lid again -- and that is well; but also she will never sit down on a cold one any more.
    -- Mark Twain, Following the Equator

Keep your childlike optimism.