Adonis is a figure in Greek Mythology most known as a beautiful youth who captured the hearts of both Aphrodite, the Goddess of Love, and Persephone, the Goddess of the Underworld and Springtime.
Adonis Syndrome can strike in proposals when you spend too much time talking about how great your NGO is. Sometimes this occurs because the writers are overconfident that their NGO is better than all the rest, but often too this occurs because the writers are not confident their NGO is the best, and so want to spend extra effort to make it look better than it is to donors. Both of these situations are problematic and will detract from your proposal.
The simple solution is to focus your proposal on the project impact and not on your NGO. It may be frustrating since NGO workers care a lot about their organizations, but donors often care more about what you can do rather than who you are. Once you build a relationship with a donor this can change, but this is generally true for any new donors you approach.
In short, do not go on and on about how great your NGO is. Donors want to hear more about your impact.