Sometimes, it is not useful when a guide writer plays a new game perfectly. In my own first game of Sunshine Islands, my first priority was to obtain as many Sun Stones as possible by befriending Characters in order to raise all of the Islands. Whenever I proposed marriage to an Eligible Bachelor, my proposal was accepted instantly.
Players began to write to me about their own inability to make a successful proposal. I always knew that a requirement of marriage was to raise Mystic Islands in order to meet the Harvest Goddess as well as Nathan and Alisa at the Church. As players wrote about their unsuccessful proposals, I began to wonder if the requirement could be wider in scope, if one had to raise ALL the Islands.
Well, one need not raise ALL the Islands before one can marry, but there are requirements that concern Sun Stones obliquely with respect to marriage. With respect to marriage to Shea, for example, you need to have obtained both Sun Stones from Shea (one as an individual and one for his 'house') as well as the Sun Stone from Wada. I would imagine that any player who has trouble with his/her proposal to another Eligible Bachelor or Girl has failed to obtain all the Sun Stones that individual and his/her family has to offer.
Thanks to the players, Adriana (NeonCrucifixion) and Shannon who discovered that Shea's 'additional' requirement for marriage was that he/she must obtain the Sun Stones both from Shea and from Wada. These Sun Stones ALL are based on Friendship Points. Another way of defining the requirement would be that the player must make certain to raise the Heart Levels of all members of the family...
It is only when players encounter problems in any game that guides can become truly comprehensive in scope.