As has been said, there are many variables. Here are a few that come to mind:
How large of a sales force does your carrier have?
Is your carrier regional or national?
How many trucks does your carrier have on compared to the number of loads to haul? (carriers sometimes over-expand their fleets)?
What are the nation's general economic conditions? (A September in an expansion will be different than a September in a recession)
If your carrier tends to haul freight for a particular economic sector (automotive for example), what are the economic conditions and cycles of that industry?
What new markets (if any) is your carrier developing?
Is your carrier's competition eating into your carrier's business? (A price cut or new service offered by a competitor this year may significantly reduce the amount of freight that was there to haul last year.)
More to the point perhaps, and more under your control, how are you and your truck equipped?
Do you have a security clearance?
Do you have the training to haul particular types of HAZMAT loads (radioactive, explosives)?
Do you limit yourself to no-touch freight only, or are you willing to load, unload, and move freight around off the truck (which would likely require you to also equip the truck with things like dollies, a pallet jack, etc.)?
Do you have a lift gate?
Do you have a reefer?
If you have a reefer, does it have the state of the art communications and temperature recording capabilities some shippers now reqire?
How large is your truck? (a large truck can haul small loads. A small truck cannot haul large loads)
Are you willing to accept loads that pay less money than you have grown accustomed to expect?
Are you willing to accept loads that take you into slower freight areas that will likely require a lot of deadhead to get out?
Are you willing to accept loads that you'll lose money on? (You asked about staying busy, not staying profitable).
Of course, the economics of such things like reefers must also be taken into account. Having one may open you to receiving more loads (reefer trucks can haul dry van loads too), but the reefer cost may or may not justify itself.
In other words, it is very difficult to predict when you'll do well (and where), and when you won't. While economic indicators make it possible to know where the economy may be going in the next few months, longer term projections are speculative at best. And even then, while the expediting industry may be booming, poor decisions at one carrier can diminish the freight that is available to you.
My wife and I take heart in the example set by long-term veterans of this industry. They are still doing it after riding out several economic cycles and carrier gyrations (some self inflicted). Of course, a large number of experienced expediters have crashed on the rocks along the way too.
Perhaps the most significant factor of all is your cash flow and capital. Low expenses and cash reserves mean a lot when freight is slow.
