Weights are initialized to small random numbers on creation (it actually depends on the type of layer you’re using but for argument’s sake we’ll just say small random numbers), usually this isn’t a huge deal as your model will eventually learn the correct weights through gradient descent. However, depending on the model complexity this may take a long time or get stuck in a local minimum. You can set the weights manually to “guide” your model to faster convergence if you have an idea on what would work better.