Recent research indicates — “confirms” is more like it, if you ask me — that lawyers, especially male lawyers, tend to be overly optimistic about their clients’ likely outcomes in litigation. See this summary in the ABA Journal of the published research findings.
This, incidentally, is a compelling reason for contract drafters to include a provision requiring early neutral evaluation (ENE) of disputes at either party’s request. Getting an early sanity check from a neutral third party can help parties settle and move on, before their attitudes start to harden and (in a classic example of the sunk-cost fallacy) their legal bills start to mount up.