Getting foundation right is harder than it looks, and almost everyone picks the wrong shade at least 3 times before figuring it out.
Testing on the wrong spot
Most beginners swatch foundation on their wrist or the back of their hand. Neither location matches your face. The skin on your jaw and neck is the correct test zone, because that is where the foundation actually needs to blend. Test 2 to 3 shades in natural light, not store lighting, and wait 2 minutes for oxidation before deciding.
Ignoring undertone entirely
A shade can match your depth perfectly but still look off because of undertone. Skin undertones fall into 3 broad categories: warm, cool, and neutral. If your veins look greenish, you lean warm. Bluish veins usually signal cool undertone. Buying a shade without checking undertone is why so many beginners end up with an ashy or orange finish.
Buying online without sampling
Ordering foundation based on a name like medium beige tells you almost nothing. At minimum, request a sample or use a store tester. If ordering online is unavoidable, check if the brand offers a shade finder tool that uses 6 or more reference questions about your skin.
The right shade should disappear into your skin, not sit on top of it.