I’ve learned a lot of lessons and made plenty of mistakes over the years. If you don’t do it right, frugality can actually end up costing you money or alienating people around you.

Here are some common frugal mistakes. Some of them I’ve made myself, some of them I’m seen others make, but all of them offer important lessons about frugal living.

1. Buying something just because it’s on sale.

It’s easy to get caught up in the mark-down of a sale item. If an item’s regular price is much higher than the sale price, it’s tempting to convince yourself that it’s a good deal. But if you don’t really need the item — if you’re only buying it because it’s marked down — then you’re actually losing money. Just because the item is 50% off doesn’t necessarily mean you can’t find it cheaper somewhere else, either. This is particularly important to remember as we head into the major post-Thanksgiving, pre-Christmas sales.

2. Compromising quality for a lower price.

I’m not talking about the subtle quality difference between name brands and generics. Most frugal folks don’t even notice a difference in that case. I’m talking about buying junk to save money. I learned this lesson the hard way when I bought ink cartridges through an online retailer, and they didn’t work. I ended up getting a refund, but the point is that I wasted a lot of time and energy on junky cartridges to save only a few dollars.

The tricky part is that it’s hard to know whether you’re buying junk or not until you’ve tried it. The best you can do is educate yourself on products and their low-cost alternatives, seek out reviews, and try to be sure you’re getting quality products at a low price. In the end, though, it takes a lot of trial and error to find a balance between quality and price. Make sure you’re not gambling on big ticket items, though.

3. Not budgeting for surprises or irregular expenses.

I love zero-based budgeting. The only problem is that it’s very easy to assign all of your income to various expenses without leaving room for irregular expenses like oil changes for the car, haircuts, or gifts. These are expenses that don’t qualify as emergencies, but don’t really fit anywhere in the monthly budget. I’ve only been sticking to a budget for about three months now, but every single month something comes up that I wasn’t expecting or that I forgot to add.

I handle it by planning for certain expenses, like car maintenance and haircuts, by putting aside a few dollars every month. I also try to leave about 5% of our income for “miscellaneous expenses.” This doesn’t always work out, but it’s a good goal to strive for. If you don’t use the money by the end of the money, throw it into savings or debt.

4. Being “cheap.”

There’s a big difference between being frugal and being cheap. To me, the difference is in the effect your behavior has on others. Frugality should never come at the expense of others. The most obvious examples of cheap behavior are stiffing a good waiter to keep a restaurant bill low or showing up to a dinner party empty handed to avoid spending money on a bottle of wine or dessert dish. There’s a good reason that cheap has a such a negative connotation.

Besides, the way I see it, frugality is a fun game. I’m constantly challenging myself to find clever ways to live well and give more to the world around me without spending a lot of money. Being cheap is cheating. Where’s the fun in that?

5. Depriving yourself.

The most important lesson I’ve learned is that frugality is a lot like dieting — if you’re too extreme, you’re probably not going to succeed. Frugality isn’t about deprivation. There are certainly sacrifices involved, but it’s important to make sure you’re not completely depriving yourself of the little things in life that makes you happy. For me, that means treating ourselves to a restaurant meal once a month, budgeting $50 a month for entertainment, and finding frugal ways to continue our favorite hobbies.