As President Eisenhower famously said, “In preparing for battle I have always found that plans are useless, but planning is indispensable.” While he was directly referring to war planning, the sentiment holds true to everyday life and finances as well. No matter how good you are at planning for what you want to have happen, what actually does happen will probably end up different. Being able to adapt your plans as reality unfolds is key to your ultimate success. When it comes to personal finance, the key to your adaptability comes from planning to live on less than you earn and socking away the extra in savings. While that savings probably won’t provide the highest rate of return in your overall asset allocation strategy, it can be an incredibly important part of keeping a small problem from becoming a big one. With that in mind, here are three expensive things that just might happen to you that you’re probably not planning for.If you haven’t reached your Social Security full retirement age yet, you need to be somewhere between 66 and 67 years old before you can hope to claim the full amount Social Security promises to pay you. In addition, if you’re expecting to rely on Medicare to help with your healthcare costs in retirement, you’ll need to be at least 65 to qualify for that coverage under most circumstances. Even if you’ve got a plan that lets you retire in that 65 to 67 age range, are you ready to leave work earlier than that? Chances are amazingly good that you’ll actually retire earlier than that, whether you want to or not. Indeed, the average age at retirement for people currently retired is just under 60 years old. In addition, the most common age to collect Social Security is 62, the earliest age you can collect retirement benefits and the age at which your monthly retirement benefits are the smallest. Importantly, there’s a significant penalty of up to $1 for every $2 you earn above $18,240 within the year if you’re working while collecting Social Security and below your full retirement age. That suggests that most of those people collecting at age 62 are doing so either because they really need the money or because they really are not expecting to go back to work. That should give you reason to pause if your current plans involve working to your full retirement age or beyond.Even if you can get through life without being affected by the substantial risks of disability or earlier-than-expected retirement, “life happens” to all of us. Cars break down. Roofs need replacing. Water heaters spring leaks. Furnaces crack heat exchangers. Short-term job losses take place, even when the overall economy is booming. People fall on the ice and break bones. There are countless ways that unpleasant surprises happen, yet around 60% of Americans can’t cover even a $1,000 emergency. That makes this one perhaps the scariest item on this list. If you’re living paycheck to paycheck to the point where you can’t cover one moderately sized unexpected expense, then when that unfortunate surprise happens to you, it becomes a double-whammy. After all, not only would you be forced to cover that unexpected cost, but also the interest payment on the credit card, cash advance, or personal loan you’d be forced to borrow to pay the bill. That makes the hole that much tougher to climb out of.