Self pity, self doubt or some elaborate form of courtship bordering on deception? We obviously cannot conclusively judge but once again Shakespeare seems to be intentionally selling himself short. Is that really appealing in a suitor?
The first line calls to fate whilst implying that spontaneous good fortune exists, " those in favour with their stars" almost as if this was a well known fact of some sort. This notion then paves the way for line 2 which on the face of it seems to be a badly veiled assertion that success or respect ( public honor and proud titles) is derived from naught but luck. Admittedly, these lines are delivered in a somewhat indifferent tone yet one just cannot ignore the bitterness these lines doubtlessly bear. It is the classical belittling of another's achievement so as to appear more significant. The product of a younger less successful Shakespeare perhaps.
Drawing on the bitterness brings forth a rather sombering realisation, an unfortunate consequence almost all of us must bear, not all of us can have proud titles so our happiness will not come from there. Instead, we can each have a lover, " ... for joy in that which I honor most," a prospect which let's be honest is not so bad.
The second quatrain describes the nature of the honor and titles those who seem favoured enjoy. Just as marigolds, they bloom ( enjoy the benefits) only when the sun shines ( only when they are still in good books with their superiors). Their worth is defined only by how the powers that be view them and should they be looked upon negatively they become worthless. A rather sad scenario for one to find himself in and yet so many of us in the modern world live under such a veil. Our worth is so often pegged by the friends from whom we seek approval, we baulk in the face of societal pressure and at a frown we , in our perceived glory die. Well defined principles and solid achievement usually solves that but not in Shakespeare's world as the third quatrain explicitly shows.
A typical warrior's career is mapped in the third quatrain. A career constantly riddled with success before just on failure comes along to erase all the good that existed before. The gist of it would be that life is unfair and there isn't room for even one mistake but behind this all too true metaphor is the implication that the persona's love for the Fair Youth is the only safe thing in this life. All else seems to be perched on a precipice; if one is lucky enough to draw honor from whence it may be drawn, it may just as quickly evaporate and even if one were to work for it, there would always be that one hurdle to trip them up. It is only in a state of reciprocated love that one can be safe, it is there alone where "one may not be removed," the only safe place in this harsh world.
So go forth to love and be loved.