Understand that freedom of choice can be both invigorating and
debilitating, it's that potent. After all, it implies that you're to make
your own decisions, and that you alone are accountable for what you do. So
even after realizing that most of the options open to us in life are ours
to follow through on or not, many of us simply don't "connect the dots."
Let's see how Rambam expands upon it.
"People often mistakenly believe" he says "that a person is compelled to
do certain things that are actually open to choice". Many suppose, he
offers, that a person is destined to marry a particular person, to be a
thief, or the like, "But that's erroneous" he says. Since contrary to
popular opinion, marriages aren't made in Heaven, and no one is
destined to be a thief or anything of the sort.
After all, it's a mitzvah to marry and a mitzvah to be honest, he points
out. And since "G-d doesn't compel you to observe mitzvot" or not, it
follows that we alone choose whom we'll marry or how honest we'll be.
(We grant you that many people are especially attracted to each other
because they have the same tastes, run in the same circles, are about the
same age, etc. But the point is that there are quite a number of people in
those categories as well, so no one is sure to marry any one of that type.
And while it might also be argued that certain people are craftier,
shrewder, have more "street smarts" than others and the like, so they're
more likely to take advantage of others' money, it's nonetheless true that
no one is impelled to either commit or be a victim of a crime.)
So Rambam reiterates that "our actions are in our own hands" and we're not
impelled to do or not do anything. In fact, the Talmudic statement cited
before that "everything is in the hands of Heaven but the fear of Heaven"
which seems to deny free will actually reinforces Rambam's arguments for
it. Let's see how.