Honestly everyone has what pushes them over the edge but the most common is the fear of failure, the never ending urge not to accept defeat, in as much as encouraging is good; it helps in pushing your mind sometimes.
Honestly good parenting friend, although I believe it's dependent on context of knowing the child's ability if he possess it already and is having a mental issue implementing it encouragement is need if otherwise dependent on gaining an ability disappointment should be used but rightly.