Adrenaline. Also our first experiences of something are hard to remember because we are vaguely monitoring how we feel because we don't know which details are variable and important yet. If you imagine the first time you had ice cream, you probably at most remembered that it was sweet and cold and you liked it. With more ice cream tastings you develop preferences and opinions, largely constructed by contrasting a lot of past experiences with each other. That's my sense at least.