In an ideal universe, dice are fair. Their results follow a uniform distribution with an equal chance to land on each face.

But we don’t live in an ideal universe. In our universe, no die has the ideal uniform distribution and equal probability of landing on each face. We know this because the distribution of rolls any given die rolls is a multivariate continuous distribution, and like any continuous distribution, the probability that the results are an exact result are always 0. Instead, to have positive probability, you have to include a range of results. So a d6 cannot have a 1/6, 1/6, 1/6, 1/6, 1/6, 1/6 distribution. Instead it can have a distribution close to the ideal distribution.

A thought experiment: In order for a die to have the ideal distribution, it has to have the ideal shape. For a d6, this is a perfect cube. Every angle has to be exactly 90 degrees and each side needs to be perfectly flat. Any imperfection will have some small effect on the chance to roll one side, and because the sides are not independent,  the chance to roll at least one other side. Given current die manufacturing technology, can this perfect die exist? Or are the best dice that have ever been made merely close to this perfect die?

So no die holds the ideal distribution. Each one instead holds its own distribution that is hopefully close to the ideal.

But it gets worse. Not only is no die ideally fair and instead holds its own distribution but no die even rolls true to its own unique distribution!

See this article from Inside Science discussing this paper from the journal Chaos.

Instead of rolling true to their own unique distribution, the result of a die roll are heavily influenced by the initial position of the throw and by the amount of bounces in the roll, which depends on the type of surface on which the die is rolled.

Consider a worst case die roll: a die is dropped straight down, does not bounce, and lands facing exactly as it was dropped.

Consider the best case: the die bounces an infinite number of times and achieves its unique distribution.

Every die roll is somewhere on a spectrum between these two options.

So dice don’t roll the ideal distribution and they don’t even roll their own unique distribution. They instead roll a distribution based on the die itself as well as the conditions of the roll.

This is a lot of words to essentially say: don’t worry too much about dice rolling ideally, because they don’t, and if you are worried about it, maybe get a dice tower with lots of baffles.