This is a slight variation on a game between me and ect on KGS. If nothing else, it goes to show that this type of situation isn't as contrived or infrequent as one might imagine.
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[19]KM[6.50]
PW[dr]PB[ect]AW[ra][mb][qb][kc][mc][oc][qc][dd][ld][nd][pd][me][pe][cf][mf][pf][jg][kg][lg][og][qg][nh][oh][di][pi][fj][gj][hj][jj][pj][hk][jk][pk][il][jl][jm][kn][on][qn][lo][mo][ro][rp][jq][kq][lq][mq]AB[na][oa][qa][nb][pb][rb][fc][hc][jc][lc][nc][pc][jd][od][fe][oe][nf][mg][ng][kh][lh][mh][ph][mi][ni][oi][kj][oj][dk][fk][gk][ik][kk][hl][cm][gm][im][jn][io][ko][cp][kp][lp][mp][pp][eq][hq][nq][qq][rq][mr][nr]C[Black has just captured the ko at Q19. Find White's largest ko threat.]PL[W]MA[pa]
(;W[np]CR[np]
;B[pa]CR[pa]C[If Black fills, what is White's follow-up?]
;W[jo]CR[jo]
;B[jp]CR[jp]C[Black clearly doesn't see O4 as a reasonable ko threat. Convince him you were right.]
;W[ip]CR[ip]
;B[jo]CR[jo]
;W[ho]CR[ho]
;B[in]CR[in]
;W[hm]CR[hm]
;B[hn]CR[hn]
;W[gn]CR[gn]
;B[hm]CR[hm]
;W[fm]CR[fm]
;B[gl]CR[gl]
;W[ek]CR[ek]
;B[fl]CR[fl]
;W[el]CR[el]C[RIGHT])
(;W[jo]CR[jo]
;B[pa]CR[pa]C[Black fills, clearly indicating that he thinks your invasion doesn't have legs to stand on. Convince him.]
(;W[np]CR[np]
;B[jp]CR[jp]
;W[ip]CR[ip]
;B[jo]CR[jo]
;W[ho]CR[ho]
;B[in]CR[in]
;W[hm]CR[hm]
;B[hn]CR[hn]
;W[gn]CR[gn]
;B[hm]CR[hm]
;W[fm]CR[fm]
;B[gl]CR[gl]
;W[ek]CR[ek]
;B[fl]CR[fl]
;W[el]CR[el]C[RIGHT])
(;W[jp]CR[jp]
;B[np]CR[np]C[Even despite the remaining atari in White's favor at K6, you should be able to do better.])
(;W[in]CR[in]
;B[jp]CR[jp]C[White has only made a small dent in Black's moyo, and your stones at the bottom are still cut from the top. You can do better.]))
(;W[of]CR[of]
;B[ne]CR[ne]C[Black would answer this, but it's not the biggest ko threat. If White recaptures the ko at Q19, Black starts a second ko at N16.])
(;W[ne]CR[ne]
;B[of]CR[of]C[Black would answer this, but it's not the biggest ko threat. If White recaptures the ko at Q19, Black captures to make an eye at Q13.])
(;W[pa]CR[pa]C[NOTTHIS]))