"understandable tendency" is a correct and usable phrase in written English.
You can use it when describing a behavior or tendency that is easily understood and makes sense given the circumstances. Example: It is an understandable tendency for people to feel anxious about starting a new job, but with time and experience, they will become more confident and comfortable.
Being in power, at local or at national level, has an understandable tendency to suck you away from reality.
In a show of such scope, there is an understandable tendency to fall back on the greatest hits.
A visiting general would not welcome tidings of torture and murder; there was an understandable tendency to recoil, because of concern about a scandal in the press.
There is an understandable tendency to pull quick and easy solutions out of the policy bag and wave them in anger to comfort and appease.
Yes, it was our finest hour but we had an understandable tendency to overstate its importance in the overall scheme of the second world war.
This compounds the understandable tendency of Chinese leaders to focus on China before they worry about the expectations of the outside world.
There are understandable tendencies among people to say, "Let's avoid conflict".
In chronicling the course of that project, Wolff's biography -- now the best in English -- might have gone farther in exploring the nature of the musical science, and less far in its understandable tendencies to hail Bach's "perfection".
The confusion is understandable, given the tendency among some of the popular media to tar all late-20th-century financiers with the same brush of infamy.
Over the years, there has been an understandable though regrettable tendency to give every umpire, even the least competent, the opportunity to work a World Series.
The biographies have been useful, because I do think that there's a tendency, understandable, to think that whatever's going on right now is uniquely disastrous or amazing or difficult.
