I certainly do at times... especially when I am teaching a child something for school for the 7th time ( i get bored with repeating basics with each child) Plus that child is struggling with the concepts and a younger sibling is getting it far more easily than the one you are trying to teach. I don't know how to help it!
I also get discouraged and unmotivated if a child is disobedient or neglectful of something that they should find easy to do. I struggle if I have a pile of washing of mountain like proportions, and then a few days later I face it all over again.
(We all have our areas of difficulty) But our areas of difficulty are part of our calling, career....here are some verses that helps me cure all lack of motivation!
For by Grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast. For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them (esv)