What make VtES hard to learn

Yes, as I said Boris...

End of a round =/= End of the Combat.

First you reach the end of the round (which will either have a "continue combat" OR "end combat"). This is when Taste of Vitae is played. After determining if the next round of combat will occur. Telepathic Tracking (at AUS) is played here (when the press step will resolve to "end of combat" and changes that to "continue combat"). Players have to have agreed that the round of combat has ended for Taste of Vitae to be played.

Psyche can only be played as the combat would end. You have the leave the "End of Round" step (where you could play Taste of Vitae) and enter the "End Combat" step (where all sorts of other "End of a Combat" cards are played). Psyche and Haven Hunting share a window. Coordinate Attacks shares the window with Psyche (again both say "at the end of combat" or "as the combat is about to end" which is not "end of round"). Apparently the Rules Team did not decide to use identical phrases, but since Coordinate Attacks has been edited to share a window with Psyche, then the longer phrase on Psyche must be equivalent to the one on Coordinate Attacks and also equivalent to the prior text of Psyche.

Coordinate Attacks
:Combat: Combat
Sanguinus
Requires a ready untapped Blood Brother of the same circle as another one you control in combat.
[san] Only usable at the end of combat if the minion opposing the Blood Brother you control is still ready. This Blood Brother taps and enters combat with the opposing minion. The first round of combat, the opposing minion cannot play any strike cards.
[SAN] As [san] above, and this Blood Brother gets an optional maneuver on the first round of combat.

(Sourced from Secret Library, which based on the "Rules" section on the left should contain the current text.)

Psyche!
Type: Combat
Requires: Celerity
[cel] Press.
[CEL] Only usable at the end of combat when both combatants are still ready. Begin another combat with the opposing minion.

(Sourced from ARDB, which was the previous edition and which would have been solved by explicitly creating an "end of combat" window inside the combat to be the combat equivalent of the "Freak Drive/Voter Cap" window for actions).

Yes, but psyche and taste of vitae are played in the same window — so in theory you could psyche and then then taste of vitae as it's still the end of a round even if combat is about to end (or a new one start in this case). Just like you can play taste of vitae after SCE.

Juggernaut1981 wrote: End of a round =/= End of the Combat.

Psyche can only be played as the combat would end. You have the leave the "End of Round" step (where you could play Taste of Vitae) and enter the "End Combat" step (where all sorts of other "End of a Combat" cards are played). Psyche and Haven Hunting share a window. Coordinate Attacks shares the window with Psyche (again both say "at the end of combat" or "as the combat is about to end" which is not "end of round").

I think Juggernaut is confusing the actual game rules (which are by no means clear and sensible and are certainly not perfect or even good for that matter) with his personal version of the rulebook that can be found on his Blog.

Juggernaut1981 wrote: (Sourced from Secret Library, which based on the "Rules" section on the left should contain the current text.)

It doesn't, at least it does not contain the last batch of errata. The .txt (from which I quoted) and .csv files on the site are up to date because Pascal maintains them. Synchronisation with the Secret Library does not depend on him.

EDIT:

PMed jhattara about it.

Juggernaut1981 wrote: Psyche!
Type: Combat
Requires: Celerity
[cel] Press.
[CEL] Only usable at the end of combat when both combatants are still ready. Begin another combat with the opposing minion.

You need to update your ARDB's DB:

Psyche!
[CEL] Only usable at the end of a round when both combatants are still ready and combat is about to end. After this round, begin another combat with the opposing minion.

Coordinate Attacks
[san] Only usable at the end of a round if the minion opposing the Blood Brother you control is still ready and combat is about to end.