Both my boys were stubborn. My best advice having dealt with it twice is to offer incentives, don't obsess over the idea and let them kind of make up their mind to do it when they are ready. If you push too hard, they will push back by not cooperating. Going potty (or not) is something they can control, and in an sense, it gives them power over you. Don't make it a battle of wills, make it a team effort.