As a former stockbroker / financial planner, I hate to admit it but a lot of retirement is luck. Saving for retirement is extremely important BUT planning is not.
You can easily see what I mean. Imagine two people with basically the same incomes (adjusted for inflation) and one person retires in 1980 and parks the bulk of their retirement money in safe CD's paying 15%! Now that is good timing but is really just plain luck, not planning.
Imagine a second guy who retired just a few years ago, in 2008, ouch, first off, he likely lost some of his retirement money in his 401k or IRA and then had the unfortunate timing to choose between a stock market that is pretty darn scary or a CD or other fixed income paying virtually nothing. This is also luck, bad luck, but again, has nothing to do with planning.
The point is that while planning is fine idea and looks good on paper, its really a useless exercise with little value. Financial planning is propagated by the investerati to keep your assets under their control.
A better idea is to be fiscally prudent (buy what you can afford), save what you can when you can (set a goal of 10%-15%), don't stress too much about retirement and when it comes time to retire, then and only then can you truly plan.
Planning when retired (or within a year at most) is infinitely more accurate, you will know what assets you have, what liabilities you have and can adjust your lifestyle to match, its that simple. In my book, How the Investment Business Really Works, I offer a worksheet in the back of the book that will walk you through the simple steps to what I call Realistic Retirement.