Eps and Ips tend to wax and wane in openly demonstrating interest in one another. They may seem to get comfortable with the other's level of interest, only to have one or both of them seem to back off. It may be something minor that instills doubt [one of them may be busy for a few days; one may make an offhand comment that throws the other off; one may not respond satisfactorily to pokes for affirmation or reassurance; etc. Possibly, neither person wants it to be overly obvious that they care as much as they do, so they withdraw or hold out in the beginning.
Ep-Ip relationships take more time to dualize than Ej-Ij relationships, and they may also be more fragile until trust is established on both sides. Although both people may want a deeply committed partner, this is sometimes veiled because neither person feels they can be sure of the other's enduring interest.
Eps are naturally attracted to Xe [their HA, Fe or Te] but Ips don't emit Xe [their creative function] at random; they use their creative function (Xe) to draw people in initially, but soon after 'hooking them' they default to Xi [their base function, Ni or Si] in order to assess the situation – Xe is subdued at that point while the base function is at work. If Xi determines that it's safe, the Ip relaxes and Xe comes out again. This may confuse the Ep, who may think the Ip is bored or has decided that the Ep wasn't all that fabulous after all.
Ips prefer being pursued by Eps, rather than pursuing. They are drawn to the Ep’s Xe [the Ep’s base function and the Ip’s DS]. However, when Eps switch to Xi [the Ep’s creative function and the Ip’s HA] to assess the relationship, it may cause confusion in the Ip: the Ep has stopped pursuing and has begun to make rational decisions about the relationship, and this can be off-putting for the Ip. Among other things, the Ip finds the Ep’s Xi much less warm than the Ep’s Xe, so it may seem that the Ep’s interest has changed for the worse.
Eps and Ips may frustrate each other very much. Neither person realizes that the other is crazy about them; they test, withdraw, pursue, etc and confuse each other very much. It will only work out if one or both of them acts naturally even if they feel vulnerable doing it. Otherwise the relationship falls apart and both of them are left thinking, they are unwanted, which is in fact untrue.