Even though ENTJ and ISTP personalities tend to get along great, it is important to note before we start that there are many other factors besides personality that influence human relationships.
Some of those factors may be: social status, sex, financial power, self-confidence, skill in a profession, popularity and any of the other real or imaginary metrics people rate themselves on.
Age is also a frequently overlooked factor (just imagine an old ISTP mechanic annoyed by a teenage ENTJ knowitall, and then imagine a young ISTP admiring his ENTJ professor's programming skills). Needless to say it's a very different relationship.
Yeah, but are they compatible?
Ok, for the purpose of explaining a sort of general compatibility of ISTPs with ENTJs we'll have to ignore a couple of factors and get on with it.
A couple of things that are in common for most ENTJs and ISTPs are:
- An admiration for and a focus on skill (technical, physical, artistic too)
- Seeing life as just a game
- Respect for logic and rationality
- Very open to new experiences (which may include dangerous physical activities in search of thrill)
- Both are able to stay calm in crisis situations
- Can handle conflict and criticism
As you may have concluded there is more than enough ground for ISTP and ENTJ peers to have fun and profit from each other. As for the downsides; in a general sense there really aren't many of them. The ego of an ENTJ is rarely bruised by an ISTP and vice versa. Assuming they are both psychologically healthy, it usually ends up being a buddy relationship without any unhealthy competition or envy.
However, any of the above mentioned factors (age, sex, status...) can have a big positive or negative impact on compatibility.