The idiom “to have too many irons in the fire” means to undertake many things or have many activities under way at one time; also, to have alternate plans for gaining one’s purpose; or, if we say “too many” rather than “many,” to be engaged in more activities than one can properly manage; to bite off more than one can chew.
The allusion in any case is to the blacksmith. He who has many irons in his forge wastes little time.
His well-trained apprentice maintains such control of the bellows and the placement of the irons that each is ready in turn at the anvil and hammer.
Or if, perchance, an armorer were engaged in forging a suit of armor, he would be ready, if skilled, to take whatever piece of steel came from the forge and shape it to best advantage, whether for greave, cuirass, vambrace, or gauntlet.
“Too many irons in the fire” would mark an inefficient smith or one with an unskilled apprentice.
Figurative use of either saying takes us back only to the middle of the sixteenth century.