The most important teaching of socionics is that we all see reality distorted according to our personal preferences. And only those who are different from us are capable of noticing it.
Since I'm a Fi valuer myself, it is my turn to explain how deformed the views of the Ti valuers are.
Ti is small scale logics and Fi is large scale logics. A Ti valuer has a natural tendency to analyze stuff in a detached way. Sees a statement and any given information and determines wheter there is coherence, validity and the like. Ti is the ability to present ideas in a way they require nothing else to be understood; encapsulated.
Fi valuers, however, do not communicate in such a way. Fi valuers have an intelligence which is associative and when presenting an idea, they simply share the filter which arranged the existing information in an specific way (Fi). Their natural interlocutor is a Te valuer, who knows a lot of information and uses the Fi filter to arrange his own information in that particular way, to arrive to the same conclusion the Fi valuer has. Te valuers analyze the factual aspect of the communication and notice when an association is being made on false grounds. They use Ti, but it is subordinated to Te.
When Fi and Ti types do not understand each other, it is always because Ti valuers are unable to compensate for information which is not explicitely shared (because they use Te, but it is ultimately subordinated to Ti), or are unable to build their own frameworks to understand the relationship between raw information when there is none given explicitely.
Conclusion: Ti is the innability to understand complex ways to handle information.