1. Missionaries are spiritual giants.
While we may feel called to go overseas, it doesn't mean the calling is any more meaningful than being called to work in the US, or wherever you currently call home. It also doesn't mean our theology is perfect. Often, it isn't, and we can learn alot about God from those around us, regardless of what culture we are in, if only we'd open our eyes.
2. Missionaries have it all together.
This, in fact, is one of the biggest myths out there. Sure, it takes a lot to give up your home and familiar surroundings and go overseas. But we all have baggage, including missionaries, and it doesn't stay at the airport when you leave. Often, living overseas can exaggerate or worsen whatever baggage you have...but I think God often uses that as a way of calling attention to those sharp edges we have that He'd like to smooth over. Often, it seems God calls the most stubborn to be missionaries because there are things He knows you have to be taken out of your comfort zone in order for you to see all your glaring faults, so he can prune those unhealthy parts of you so you can grow back healthier and stronger.
3. Working overseas is glamorous.
Sure, those of us who have worked overseas have our stories..."one time someone brought me a boa constrictor in a jerry can and wanted to sell it to me as a pet"..."I was once monkey-slapped by my neighbors pet monkey"..."we went on a jungle walk and ate fresh cacao fruit".
These stories seem great, but it's just a small part of life overseas. It's still life, just not in one's home culture. There are still ups and downs, joys and pains. Sometimes, the pains seem to come more frequently than the joys. There is conflict, more often with other missionaries than with the nationals you live among. This conflict can seriously impact the ministry you are trying to build. There are cultural misunderstandings, which at times can lead to broken relationships with those among whom you are trying to build relationships.
If you're a medical missionary, there is much sickness and death, frustration at diseases that could be treated easily in your passport culture (where you were born and raised) but are not so easily treated in your host culture. This could be due to late presentation (coming in for care too late in the disease process to be able to treat), lack of resources/equipment to treat the disease, or lack of financial ability to pay for the needed treatment.
There are joys as well, such as a malnourished child being nursed back to health-watching the fog in their eyes lift as their body gets proper nutrition, and then seeing them continue to do well after hospital discharge. Or the woman you admitted whom you thought would die over the weekend, and miraculously not only survives to hospital discharge, but thrives afterwards from accepting Christ as her Lord and Savior. Or the joy of seeing 1.4 kg preemie gaining weight, and discharged to home and doing well in follow-up...if only it was easier to remember the joyous occasions rather than the sad ones!