Does it matter what range of resistor values you use for a voltage divider, whether it's in the tens, hundreds, or thousands of ohms range?

I've run into this problem twice, once a few months ago and once just last week. If I used a certain range of resistor values for a voltage divider, the voltage at the output would not be what is expected. However, if I changed this range, the voltage would be what is expected from calculations.

How does this work? My circuits course never covered low level things like this, only things as high level as Vout = Vin * (R-from-out-to-ground / (R-from-out-to-ground + R-from-in-to-out)).

I've run into this problem twice, once a few months ago and once just last week. If I used a certain range of resistor values for a voltage divider, the voltage at the output would not be what is expected. However, if I changed this range, the voltage would be what is expected from calculations.

How does this work? My circuits course never covered low level things like this, only things as high level as Vout = Vin * (R-from-out-to-ground / (R-from-out-to-ground + R-from-in-to-out)).