Many veterans claims are lost due to a lack of sufficient evidence to prove the effects their individual service connected disabilities impact their ability to perform work that produces wages above poverty wages.
Use affidavits from relatives and friends describing in detail the difficulty you have performing ANY activity. This puts the onus on the VA to show why these difficulties do not prevent substantial gainful employment. The submission of such lay evidence of the combined effects of multiple service connected disabilities provokes the VA to produce contrary evidence and without such evidence the Board of Veteran Appeals is unable to arbitrarily reject your lay evidence. To do so, is error by the Board.
Of course it is more persuasive to have a doctor review the affidavits and opine that you are unable to perform substantial gainful employment resulting in the earning of income in excess of poverty wages.
It is best to have an experienced Veteran Disability Lawyer help you to provide and argue this evidence.