If you are investing over the long term, once you have a base
of investments, you almost always have a gain to cash in because the market generally goes up over a longer term.
For example - if you bought something in 2015 and decided to donate something in late 2018, you would most likely have a gain in that holding, even though the market was down in 2018, and could still donate it.
If there was a situation where I couldn't DIK, I would pay cash. I can't remember the last time I didn't do a DIK.
Remember. No one should invest money they can't afford to lose.