How Many Smartphone App Clicks is Too Many?

At what point will the user of a smartphone app just give up and move on to the next app? It's an important question for app developers. 
Although it's difficult to come up with an exact answer, we can understand at least something about the factors involved and how we might improve that chances that an app user will have a satisfying, non-frustrating experience.

First, there are factors that are out of the control of the developer:
Situational Pressure.
Smartphones are generally used in a higher pressure environment than is the case with a PC. People are one the move, busy and anxious to get results as fast as possible.
Information Needs.
How badly the user needs the information provided by an app will be highly variable. If they're late for a meeting and need a phone number or address quickly, user tolerence for clicking through multiple screens and waiting through delays in displays will be quite low.
App Knowledge.
All app developers would like users to take the time to completely understand every aspect of how to use their app. This usually is not the case. Users learn only the minimum they need and want apps to respond quickly.
Given this challenging environment, app developers need to focus on what they can control to make an app as usable as possible:
Apps need to be understood quickly and easily. Navigation, layout, colors, text, images, buttons ... all the elements of design play a role in creating a good user experience.
Information Load.
Is the user presented with just the right amount of information necessary to get the job done? Too much or too little can lead to an unsatisfactory experience and poor app ratings.
Click Sequences.
Can the user get to what they need directly? Having to click through long sequences of screens can frustrate users. People are impatient. 
In summary, app developers need to focus on what they can control and not assume favorable conditions for those factors that are out of their control.