A dog’s main way of learning is through repetition and association.
Typically, when you take your dog to the vets, it will be due to an issue with them or they are going in for their yearly jabs. This can easily result in the dogs developing fear and anti association towards the vets and can thus, make the experience very difficult.
A little tip to help curb this is to now and then pop into your local vets and walk them onto the scales (most vets have these in the waiting rooms), take a note of their weight which is always helpful, and then walk out with some praise and a treat after. This helps break any possible negative association they might develop.