That's absolutely correct. The tax system tends to draw a distinction between personal expenses and business or income-generating expenses, and unless there is some specific provision in the act that allows for a deduction—the tax credits are an example—to offset purely personal expenses, the tax system does not, as a general rule, recognize that. Likewise, we're taxed on our income from a business or employment or property, so expenses incurred to earn that income are deductible against that source of income.
When you have mixed activities as you do here, where you have a first aid course that could be taken for the purpose of enhancing an employer's business, obviously you don't forget that training the second you walk out the door. You have that knowledge and you have that course and you can apply it.