Your words well describe the US Revolutionary War, from 1775 to 1781, which would have ended in defeat at Valley Forge in 1778 without increasingly massive aid -- money, weapons, foreign navy, troops & diversion attacks -- from major powers like France, Spain and the Netherlands.
Our side never knew when, or how much, aid would arrive so all we could do was hang in there, keep fighting and trusting in "Providence" that enough help would arrive soon enough to make a difference.
And in the end, it did, miraculously.
Of course, even in 1783 the Revolutionary War was not fully won or over -- that took another 30+ years, until the Treaty of Ghent after the War of 1812.
So, there's no doubt that it can be very tough for a weaker military to win its war of independence against a supposed global superpower.
But it can be done.
Our ancestors did it, with a lot of help, and so, with Providence, Ukraine may also succeed.
1781 Battle of the Chesapeake,
French navy victory was key to US/French victory at Yorktown:
1814 John Quincy Adams signs the Treaty of Ghent,
ended 40 years of hostilities between the US and GB/UK:
