Following the news that bull markets make people more likely to retire -- and that doing so can put their future finances in danger -- it's important for savers to review how market returns can affect their retirement planning. On one hand, it's understandable why more retire during strong market conditions: People have a retirement savings target in mind, and bull markets can help more people reach those targets. The problem is, given the normal cycles of market returns, retiring at a peak could leave you vulnerable to the next bear market. Ideally, you shouldn't let recent returns influence your retirement planning too much. Keep these six things in mind when a run of good returns has you thinking you should retire a little early.