Crab I'm not sure what YOU mean by a discontinuity
discontinuity (dɪsˌkɒntɪˈnjuːɪtɪ)
n, pl -ties
1. lack of rational connection or cohesion
2. a break or interruption
3. (Mathematics) maths
a. the property of being discontinuous
b. the point or the value of the variable at which a curve or function becomes discontinuous
See #2
When you did your FI course you probably drew the power required curve and explained the different elements - the 3 elements are additive and that makes the graph very tall if you draw it correctly - therefore in order to get it on a normal page/board/slide, a discontinuity is inserted in the Y axis to compress the graph.
BTW - there isn't a 'gentle' arrival at the Y axis - if you include ground effect, the power required curve dips down again as it approaches the Y axis.