A lot of people look at retirement through rose-colored glasses. They envision leaving the workforce on their own terms for a life of leisure, but the reality often isn't that picturesque. Life takes some unexpected turns, and you have to be able to pivot as they occur.

Being too optimistic in your retirement planning could come back to bite you in the long run. If you're guilty of any of the following three things, you might want to rethink your strategy.

Couple looking at receipts in front of laptop.

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1. Expecting to work as long as you would like

You might have a retirement date marked on your calendar, or you might plan to work indefinitely. But there's no guarantee that things will turn out either way.

You might be healthy now, but illnesses or injuries could spring up in the future. If they're severe, they could prevent you from working.

And even if you remain healthy, that's no guarantee your family members will. You might need to quit or reduce your hours to care for others. Job loss is always a possibility, too.

If any of these things happen, you'll need a backup plan. You might be able to find another job, assuming you're still able to work in some capacity. Looking for something remote or part-time might suit you better than traditional employment if you have to work around doctor visits or caretaking duties. 

Those who aren't able to work at all will have no choice but to rely upon their personal savings and the help of family or friends. That's why it's crucial to save as much as you're able to during your working years just in case you need it. You can always pass the money on to your heirs if you don't use it all. 

2. Planning for a high rate of return on your investments

The stock market has averaged about a 10% average annual rate of return over the long term, but every year is different. Over the last three decades, the S&P 500 has seen years where it's gained over 30% and years where it's lost over 30% -- and everything in between. There's no way to predict what kind of a return you'll get in a given year or overall, so it's usually best to be conservative in your estimates.

You might not earn a 10% average annual rate of return over the course of your entire career because you won't have all your savings in stocks the entire time. As you age, you generally want to move more of your savings into safer investments like bonds to protect what you have. These are less volatile, but they also offer lower annual rates of return.

When planning for retirement, you might want to use a 5% or 6% estimated annual rate of return. Your savings could grow more quickly than this, and if they do, that's great. But if they don't, you won't have to worry about falling behind on your savings goals.

3. Assuming Social Security will cover the majority of your retirement expenses

Social Security was designed to cover only about 40% of pre-retirement income for average earners. It might cover more for some people, but nearly everyone will still need personal savings to supplement it.

This is especially true for workers who aren't yet old enough to claim Social Security. The program's trust funds are expected to be depleted within the next 9 to 12 years. Once this happens, the Social Security Administration will no longer be able to pay out all scheduled benefits unless the government takes steps to fix the funding shortfall before then. 

Even in the worst-case scenario, you'll still receive some money from Social Security in retirement. But since we don't know how this funding crisis is going to play out, it's best to reduce our reliance on it as much as possible. Build up your personal savings as much as you can and choose your Social Security claiming age strategically so you can squeeze the most money possible out of the program.

Avoiding these three assumptions isn't a guarantee that you won't experience financial setbacks in retirement. It's a good start, but you still need to have at least annual check-ins with yourself both while you're working and in retirement.

Look over what you've accomplished or spent in the last year and how that compared with your expectations for the year. If anything's off, make corrections before small issues become larger ones.