The Wide-Scope view of instrumental reason holds that you should not intend an end without also intending what you believe to be the necessary means. This, the Wide-Scoper claims, provides the best account of why failing to intend the believed means to your end is a rational failing. But Wide-Scopers have struggled to meet a simple Explanatory Challenge: why shouldn't you intend an end without intending the necessary means? What reason is there not to do so? In the first half (...) of this paper, I argue that the Wide-Scope view struggles to meet this challenge because it takes the principles of instrumental reason to have unlimited application—to apply to all agents, in all circumstances. I then go on to offer a new account of these principles. The new account is very much in the spirit of the Wide-Scope view, and shares its central advantages, but lacks its unlimited application. This view should, therefore, find the Explanatory Challenge more tractable. In the second half of the paper, I argue that this prediction is confirmed. If the requirements of instrumental reason apply only when a means is, or is believed to be, necessary for your end, then plausible independent claims, about reasons, rationality, and intentions, explain why failing to intend the necessary means to your ends is a rational failing. (shrink)