You know you are a missionary if you have suffered severe physical hardship for the cause of Christ. Remember Paul's testimony in 1 Cor. 11:
23 Are they ministers of Christ? (I speak as a fool) I am more; in labours more abundant, in stripes above measure, in prisons more frequent, in deaths oft.
24 Of the Jews five times received I forty stripes save one.
25 Thrice was I beaten with rods, once was I stoned, thrice I suffered shipwreck, a night and a day I have been in the deep;
26 In journeyings often, in perils of waters, in perils of robbers, in perils by mine own countrymen, in perils by the heathen, in perils in the city, in perils in the wilderness, in perils in the sea, in perils among false brethren;
27 In weariness and painfulness, in watchings often, in hunger and thirst, in fastings often, in cold and nakedness.
Just yesterday evening in training union I saw a video of a missionary to Peru and an American companion who go into the jungle about once a year to seek out an unreached, uncontacted tribe to give them the Gospel. In their 2014 trip they were unable to find the tribe for which they searched. Traversing for weeks the most difficult river they had ever yet found in the jungle, they eventually ran out of their rice and other food. Killing a crocodile with a sheath knife for food, they later prayed for days for food until they were able to catch a fish. Their video camera gave out, as did their communications gear and their GPS. Though completely exhausted, they were able to climb a 30 foot cliff, only to see a huge, uncrossable valley.
There they were, lost in the jungle without food, helpless before God. All that was left was prayer. Unknown to them, their contact in civilization began to worry about them, and hired a jungle pilot to find them. Knowing the general area they had gone to, the pilot was finally able to find them, drop them some food, and later land his seaplane on the river to rescue them.
Was their trip in vain, since they were unable to find the tribe for which they searched? No, not at all. Seeing the foreign missionaries go into the jungle, the national Christians said among themselves, "We should be the ones doing this." Later, the national Christians were able to make first contact with that tribe, and give them the Gospel!