In a market where firms reach a Nash Equilibrium, what is the underlying reason that prevents any firm from changing its strategy unilaterally?

In a market where firms reach a Nash Equilibrium, each firm has chosen a strategy that works best for them, given the strategies of the other firms. This means that if one firm decides to change its strategy on its own, it would not improve its situation because the other firms would still stick to their current strategies. For example, imagine two companies that both produce a similar product. If one company tries to lower its prices to attract more customers while the other keeps its prices the same, the first company might end up losing money without gaining enough customers to make up for it. Therefore, the reason firms do not change their strategies is that doing so would not lead to a better outcome for them when considering how others are behaving.